Fuel cell systems produce electrical energy through the oxidation and reduction of a fuel and an oxidant. Hydrogen, for example, may be used to produce electricity efficiently in a fuel cell. Vehicles powered by hydrogen fuel cells are often more efficient and generate fewer emissions than vehicles employing internal combustion engines.
In a typical fuel cell system, hydrogen or a hydrogen-rich gas is supplied as a reactant through a flowpath to an anode side of a fuel cell and oxygen is supplied as a reactant through a separate flowpath to a cathode side of the fuel cell. Catalysts, often in the form of a noble metal, such as platinum, are typically placed at the anode and cathode to facilitate the electrochemical conversion of the reactants into electrons and positively charged ions (for the hydrogen) and negatively charged ions (for the oxygen). In some fuel cells, the anode and cathode may be made from a layer of electrically-conductive gas diffusion media (GDM) with the catalysts deposited thereon to form a catalyst coated diffusion media (CCDM). An electrolyte layer (also called an ionomer layer) may be used to separate the anode from the cathode to allow for the selective passage of ions from the anode to the cathode while simultaneously prohibiting the passage of the generated electrons
Such electrons are forced to flow through an external electrically-conductive circuit (such as a load) to perform useful work before recombining with the charged ions at the cathode. The combination of the positively and negatively charged ions at the cathode results in the production of water as a by-product of the reaction. In another typical fuel cell, the anode and cathode may be formed directly on the electrolyte layer to form a layered structure known as a membrane electrode assembly (MEA).
Proton exchange membrane (PEM) fuel cells have shown particular promise for use in vehicles. The electrolyte layer of a PEM fuel cell is a solid proton-transmissive membrane, such as a perfluorosulfonic acid membrane (PFSA). Regardless of whether the above MEA-based approach or CCDM-based approach is employed, the presence of an anode separated from a cathode by an electrolyte layer forms a single PEM fuel cell. A plurality of such cells can be combined together to form a fuel cell stack in order to increase the power output.
The individual cells of fuel cell stacks are typically compressed together under high forces, both to ensure that proper electrical contact is made to enable drawing current from the stack and to create seals between various headers and/or conduits within the stack used to deliver the reactants and coolants through the stack. Insulating plates are often used in such stacks in order to electrically insulate one or more of the cells and/or current collecting elements from other components of the stack, such as from an end unit assembly or frame plate. Insulating plates have typically been formed from a plastic material and the adjacent end unit/frame plates have typically been formed from aluminum castings, forgings, or stampings.
Such designs may sometimes be less than ideal due to unbalanced forces on opposite sides of the insulating plate, which may result in flexing of the plate and/or a seal that may lack a desired seal compression and therefore be prone to leakage and/or failure. In order to ensure that the headers/conduits maintain a proper seal, some fuel stacks have been manufactured by bolting or otherwise fastening the plastic insulating plate to an adjacent aluminum end/frame plate with mechanical fasteners. Such designs remain less than ideal in that, for example, they often require many fasteners and other parts, they may still be configured with an undesirable interdependence between load balancing of adjacent seals, and they may still fail to adequately prevent flexing and/or offloading of seals between the insulating plate and the adjacent end/frame plate.
The present inventor has therefore determined that it would be desirable to provide methods, apparatus, and systems for improving and/or simplifying one or more seals between various plates/units of a vehicle fuel cell stack that overcome one or more of the foregoing limitations and/or other limitations of prior art.